KR101783527B1

KR101783527B1 - Scroll compressor

Info

Publication number: KR101783527B1
Application number: KR1020150165052A
Authority: KR
Inventors: 마사미 오노; 사토시 고우무라; 아키오 사이키; 도시유키 반노; 신스케 아소우
Original assignee: 가부시키가이샤 도요다 지도숏키
Priority date: 2014-11-28
Filing date: 2015-11-24
Publication date: 2017-09-29
Also published as: KR20160064986A; DE102015120389B4; DE102015120389A1; JP6394888B2; JP2016102483A

Abstract

The scroll compressor includes a rotary shaft, an eccentric shaft, a bushing, and a counterweight. The rotary shaft is rotatably supported by the housing. The eccentric shaft is displaced from the rotation axis of the rotary shaft. The inner circumferential surface of the housing has a center coinciding with this axis of rotation. The bushing rotates about the eccentric shaft in the first swinging direction and in the second swinging direction opposite to the first swinging direction. When the bushing is pivoted in the first pivot direction, the bushing has a center that is set to gradually approach the rotational axis of the rotary shaft. The counterweight has at least a radial extension extending radially outwardly from a first imaginary circle having the same center as the center of the bushing in the portion on the leading side in the first oscillating direction.

Description

[0001] SCROLL COMPRESSOR [0002]

The present invention relates to a scroll compressor.

For example, Japanese Unexamined Patent Publication No. Hei. A typical scroll compressor as disclosed in 2013-204568 includes a fixed scroll fixed to the housing, and a movable scroll configured to orbit with respect to the fixed scroll. The fixed scroll includes a fixed base plate and a fixed spiral wall extending from the fixed base plate. The movable scroll includes a movable base plate and a movable spiral wall extending from the movable base plate. A fixed spiral wall and a movable spiral wall that mesh with each other define a compression chamber. The orbital motion of the movable scroll reduces the volume of the compression chamber and compresses the refrigerant in the compression chamber.

The housing rotatably supports the rotary shaft. The rotary shaft includes an eccentric shaft projecting toward the movable scroll. The rotation axis of the eccentric shaft is displaced from the rotation axis of the rotary shaft. The eccentric shaft is fitted to the bushing, and the counterweight is formed integrally with the bushing. When the movable scroll orbits, the counterweight counteracts the centrifugal force acting on the movable scroll to reduce the unbalanced amount of the movable scroll. The bushing includes an eccentric hole arranged in an eccentric position relative to the center of the bushing. The eccentric shaft is fitted to the eccentric hole to allow the bushing to oscillate about an eccentric shaft.

The cylindrical boss protrudes from the movable base plate, and the bushing is inserted into the boss through the bearing. The center of the movable base plate coincides with the center of the bushing. The center of the bushing is located radially outward of the rotary shaft from the rotary axis of the rotary shaft. The distance between the center of the bushing and the axis of rotation of the rotary shaft is the orbital radius of the movable scroll. When the bushing swings about the eccentric shaft, the distance between the center of the bushing and the rotation axis of the rotary shaft changes. This changes the orbit radius of the movable scroll. In other words, the eccentric shaft, bushing, and bearing form a so-called drive crank mechanism that alters the orbital radius of the movable scroll. Such a drive crank mechanism is already well known.

Since slight machining errors and assembly errors occur in the movable and stationary scrolls, a backlash is provided between the movable and fixed spiral walls. When the rotary shaft rotates forward, the bushing swings to the center of the eccentric shaft by a compression reaction force acting on the movable scroll. This increases the distance between the center of the bushing and the axis of rotation of the rotary shaft, thereby increasing the orbital radius of the movable scroll. This allows the movable spiral wall to contact the fixed spiral wall, while the movable scroll orbits while the movable spiral wall contacts the fixed spiral wall. Thus, the leakage of the refrigerant from the compression chamber is limited.

When the movable scroll is mounted on the fixed scroll, the bushing is pivoted about the eccentric shaft in the direction opposite to the direction in which the bushing swings when the rotary shaft rotates forward. This reduces the distance between the center of the bushing and the axis of rotation of the rotary shaft, thereby reducing the orbital radius of the movable scroll. Thus, the position of the movable spiral wall relative to the fixed spiral wall can be set such that the movable spiral wall does not contact the fixed spiral wall. Thus, the movable scroll is easily mounted on the fixed scroll.

When the centrifugal force acting on the movable scroll increases at a particularly high rotational speed, the unbalance amount of the movable scroll increases. This increases the noise when the movable scroll orbits. Therefore, it is desirable to reduce the imbalance amount of the movable scroll by enlarging the size of the counterweight so as to reduce the noise.

It is therefore an object of the present invention to reduce the unbalanced amount of the movable scroll without extending the scroll compressor.

To achieve the above object and in accordance with an aspect of the present invention, a scroll compressor includes a stationary scroll, a movable scroll, a compression chamber, a rotary shaft, an eccentric shaft, a bushing, and a counterweight. The fixed scroll is fixed to the housing and has a fixed spiral wall. The movable scroll has a movable spiral wall that engages the fixed spiral wall. The compression chamber compresses the refrigerant by reducing the volume of the compression chamber by orbital motion of the movable scroll relative to the fixed scroll. The rotary shaft is rotatably supported by the housing. The eccentric shaft extends from the rotary shaft of the rotary shaft in a displaced position toward the movable scroll. The bushing is fitted to the eccentric shaft and rotates about the eccentric shaft. The counterweight is integrally formed with the bushing. The housing has a receiving wall having an inner circumferential surface with a center coinciding with the axis of rotation of the rotary shaft and receiving the counterweight. The bushing rotates about the eccentric shaft center in the first swinging direction and in the second swinging direction opposite to the first swinging direction. The bushing has a center which is set so as to gradually approach the rotation axis of the rotary shaft when the bushing swings in the first swinging direction. The counterweight has at least a radial extension extending radially outwardly from a first imaginary circle having the same center as the center of the bushing in the portion on the leading side in the first oscillating direction.

Other aspects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention .

The invention will be best understood by reference to the following description of the presently preferred embodiments, as well as the appended drawings, together with objects and advantages thereof.

1 is a side sectional view of a scroll compressor according to a first embodiment,
2A is a perspective view of a scroll taken along the line 2a-2a of FIG. 1, illustrating the bushing pivoting about an eccentric shaft in a direction in which the bushing oscillates to increase the distance between the center of the bushing and the rotation axis of the rotary shaft; Sectional view of a portion of the compressor,
Figure 2b is a cross-sectional view of a portion of a scroll compressor illustrating the bushing pivoting about an eccentric shaft in a direction in which the bushing oscillates to reduce the distance between the center of the bushing and the axis of rotation of the rotary shaft,
3 is a cross-sectional view centering on a bushing according to the second embodiment.

The scroll compressor 10 according to the first embodiment will now be described with reference to Figs. 1 to 2B. The scroll compressor (10) according to the present embodiment is used in an automotive air conditioner.

1, the scroll compressor 10 includes a housing 11 including a center housing member 12 (shell), a front housing member 13, and a rear housing member 14. As shown in Fig. The center housing member 12 has a cylindrical, closed end. The front housing member 13 has a cylindrical and closed end. The rear housing member 14 has a cylindrical and closed end. The front housing member 13 is coupled to one end of the center housing member 12 and the rear housing member 14 is coupled to the other end of the center housing member 12. [ The center housing member 12 is opened toward the front housing member 13 and is formed integrally with the fixed scroll 15. [ The fixed scroll (15) is located inside the center housing member (12). The stationary scroll 15 includes a disk-shaped stationary base plate 15a serving as a bottom wall of the center housing member 12 and a stationary spiral 15a extending from the stationary base plate 15a toward the front housing member 13. [ Wall 15b.

The center housing member (12) receives the movable scroll (16). The movable scroll 16 includes a disk-shaped movable base plate 16a and a movable spiral wall 16b extending from the movable base plate 16a toward the fixed base plate 15a. The fixed scroll (15) is arranged to face the movable scroll (16). The fixed spiral wall 15b and the movable spiral wall 16b are engaged with each other. The distal end surface of the fixed spiral wall 15b contacts the movable base plate 16a. The distal end surface of the movable spiral wall 16b contacts the stationary base plate 15a. The fixed base plate 15a, the fixed spiral wall 15b, the movable base plate 16a, and the movable spiral wall 16b define the compression chamber 17.

The front housing member 13 rotatably supports the large diameter portion 18a of the rotary shaft 18 through the radial bearing 19. [ The small diameter portion 18b of the rotary shaft 18 has a distal end operatively coupled to the engine E of the vehicle as an external drive source through the power transmission mechanism PT. The eccentric shaft 20 is integrally formed on the large diameter portion 18a of the rotary shaft 18. [ The eccentric shaft 20 is arranged at a displaced position from the rotation axis L1 of the rotary shaft 18 and extends from the rotary shaft 18 toward the movable scroll 16. [ In particular, the eccentric shaft 20 extends from the end surface 18c of the large diameter portion 18a facing the movable scroll 16. [

The eccentric shaft 20 is fitted to the bushing 22. The counterweight 21 is formed integrally with the bushing 22. The counterweight 21 cancels the centrifugal force acting on the movable scroll 16 when the movable scroll 16 orbits. This reduces the amount of unbalance of the movable scroll 16. The bushing 22 includes an eccentric hole 22h arranged at a displaced position from the center L2 of the bushing 22. [ The eccentric shaft 20 is fitted to the eccentric hole 22h to allow the bushing 22 to swing about the eccentric shaft 20. The center L2 of the bushing 22 is displaced from the center axis of the eccentric shaft 20. [

The rotary shaft 18 includes a recess 18d shaped like a circular hole on the end surface 18c of the large diameter portion 18a. The insertion pin 22a inserted into the recess 18d protrudes from the end surface of the bushing 22 facing the large diameter portion 18a of the rotary shaft 18. The insertion pin 22a contacts the inner wall of the recess 18d to limit the extent to which the bushing 22 pivots about the eccentric shaft 20.

The cylindrical boss 16c protrudes from the movable base plate 16a. The bushing 22 is inserted through the bearing 23 into the boss 16c. The bushing 22 supports the movable base plate 16a through the bearing 23 so that the movable base plate 16a rotates relative to the bushing 22. The center L2 of the bushing 22 is located radially outward from the rotation axis L1 of the rotary shaft 18. [ The center of the movable base plate 16a coincides with the center L2 of the bushing 22. The distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18 is the orbital radius of the movable scroll 16. [ The swinging of the bushing 22 about the eccentric shaft 20 changes the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18. [ Therefore, the orbital radius of the movable scroll 16 is variable. In other words, the eccentric shaft 20, the bushing 22, and the bearing 23 form a so-called drive crank mechanism that alters the orbital radius of the movable scroll 16. Such a drive crank mechanism is already known.

The front housing member 13 has a cylindrical receiving wall 13a for receiving the counterweight 21 therein. The receiving wall 13a has an inner circumferential surface 13b having a center coinciding with the rotation axis L1 of the rotary shaft 18. [ The receiving wall 13a surrounds the boss 16c. The rotation blocking mechanism 26 is arranged between the movable base plate 16a and the receiving wall 13a (front housing member 13). The rotation blocking mechanism 26 includes a plurality of recesses 27 (six recesses in this embodiment), fins 28, and ring members 29. The recesses 27 are arranged in the outer circumferential portion of the end surface of the movable base plate 16a facing the receiving wall 13a, and each recess 27 is shaped like a circular hole. The fins 28 protrude from the end surface of the receiving wall 13a facing the movable base plate 16a. The ring members 29 are fitted to the respective recesses 27. Fins 28 are inserted into the respective ring members.

The suction chamber 30 is defined between the outer circumferential wall of the center housing member 12 and the outermost circumferential portion of the movable spiral wall 16b. The outer circumferential wall of the center housing member (12) includes a suction port (31) communicating with the suction chamber (30). The fixed base plate 15a includes a discharge port 32 communicating with the compression chamber 17. [ The discharge port 32 is selectively opened or closed by the discharge valve 33 fixed to the fixed base plate 15a. The opening degree of the discharge valve 33 is limited by the retainer 34 fixed to the fixed base plate 15a. The discharge port 32 communicates with the discharge chamber 35 defined by the center housing member 12 and the rear housing member 14. The rear housing member 14 includes an outlet 36 communicating with the discharge chamber 35. The outlet port 36 and the suction port 31 communicate with an external refrigerant circuit (not shown).

2A and 2B, the bushing 22 rotates the eccentric shaft 20 in the first swinging direction R1 and in the second swinging direction R2 opposite to the first swinging direction R1 You can rock around. The center L2 of the bushing 22 gradually approaches the rotation axis L1 of the rotary shaft 18 when the bushing 22 swings in the first swinging direction R1. In other words, the first swinging direction R1 is a swinging direction that reduces the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18. [ The center L2 of the bushing 22 gradually moves away from the rotation axis L1 of the rotary shaft 18 when the bushing 22 swings in the second swinging direction R2. In other words, the second swinging direction R2 is a swinging direction for increasing the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18. [

The counterweight 21 has a radial extension extending radially outward from the first imaginary circle C1 having the same center as the center L2 of the bushing 22 at the portion on the leading side in the first swinging direction R1 And a portion 21a. The first imaginary circle C1 travels through a portion of the outer circumferential surface of the counterweight 21 having the smallest radius from the center of the first imaginary circle C1 (i.e., the center L2 of the bushing 22) do. The outer circumferential surface 21b of the radial extension 21a is a semicircular outer circumferential surface of the counterweight 21 and extends along a second imaginary circle C2 having a larger radius than the first imaginary circle C1. The center P2 of the second virtual circle C2 is displaced from the center L2 of the bushing 22 toward the first swinging direction R1.

The counterweight 21 has a first edge 21c and a second edge 21d. The first edge 21c is located at the end on the leading side in the second swinging direction R2 on the outer circumferential surface of the counterweight 21. The second edge 21d is located at the end on the leading side in the first swinging direction R1 on the outer circumferential surface of the counterweight 21. The centers of the first edge 21c, the second edge 21d and the first virtual circle C1 (the center L2 of the bushing 22) and the center P2 of the second virtual circle C2 are common Line. The first edge 21c is located on the first imaginary circle C1 and the second imaginary circle C2. The center of the first imaginary circle C1 (the center L2 of the bushing 22) and the center P2 of the second imaginary circle C2 Are arranged on a common line. The first imaginary circle C1 and the second imaginary circle C2 are arranged such that the first imaginary circle C1 is in contact with the second imaginary circle C2 from the first edge 21c to the inside of the second imaginary circle C2 And is positioned. The amount of extension of the radially extending portion 21a extending radially outward from the first imaginary circle C1 increases toward the reading layer in the first swinging direction R1.

The operation of this embodiment will now be described.

Since slight machining errors and assembly errors occur in the movable scroll 16 and the fixed scroll 15, a backlash is created between the movable spiral wall 16b and the fixed spiral wall 15b.

As shown in Fig. 2A, the driving force of the engine E is transmitted to the rotary shaft 18 through the power transmission mechanism PT, so that the rotary shaft 18 is rotated forward. At this time, the bushing 22 is oscillated about the eccentric shaft 20 in the second swinging direction R2 by the compression reaction force acting on the movable scroll 16. [ The distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18 is increased to increase the orbit radius of the movable scroll 16. [ The bushing 22 is limited from pivoting about the eccentric shaft 20 and the orbital radius of the movable scroll 16 is limited by the radius of the eccentric shaft 20 when the movable spiral wall 16b contacts the fixed spiral wall 15b .

The rotation of the rotary shaft 18 is transmitted to the movable scroll 16 via the eccentric shaft 20, the bushing 22 and the bearing 23 so that the movable scroll 16 rotates forward. At the time when the movable spiral wall 16b contacts the fixed spiral wall 15b, the pins 28 contact the respective ring members 29 and the rotation of the movable scroll 16 is blocked. This allows the movable scroll 16 to orbit only in the forward direction. Thus, the movable scroll 16 orbits in the forward direction, while the movable spiral wall 16b contacts the fixed spiral wall 15b. Thus, the leakage of the refrigerant from the compression chamber 17 is limited, and the volume of the compression chamber 17 is reduced to compress the refrigerant.

2B, when the movable scroll 16 is mounted on the fixed scroll 15, the bushing 22 is rotated in the direction in which the bushing 22 swings when the rotary shaft 18 rotates forward In the first swinging direction R1, which is the opposite direction to the eccentric shaft 20, as shown in Fig. The distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18 decreases and the orbital radius of the movable scroll 16 decreases. Thus, the movable spiral wall 16b is arranged with respect to the fixed spiral wall 15b in a position where the movable spiral wall 16b does not contact the fixed spiral wall 15b. This allows the movable scroll (16) to be easily mounted on the fixed scroll (15).

When the bushing 22 contacts the recess 18d while the bushing 22 swings about the eccentric shaft 20 in the first swinging direction R1 and the insertion pin 22a contacts the recess 18d, And the orbital radius of the movable scroll 16 is fixed. This allows the bushing 22 to rotate about the center L2 of the bushing 22 and the rotation of the rotary shaft 18 when the bushing 22 swings about the eccentric shaft 20 in the first swinging direction R1. Is limited from swinging about the eccentric shaft (20) beyond the position for increasing the distance between the axis (L1). In other words, when the bushing 22 swings around the eccentric shaft 20 in the first swinging direction R1, the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18 The insertion pin 22a comes into contact with the recess 18d. This limits the bushing 22 from further oscillating about the eccentric shaft 20 in the first swinging direction R1. 2B illustrates a state in which the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18 is the shortest.

For example, it is assumed that the entire circumferential direction of the outer circumferential surface of the counterweight 21 passes through the first virtual circle C1 having a center coinciding with the center L2 of the bushing 22. To limit the leakage of refrigerant from the compression chamber 17, the movable spiral wall 16b preferably contacts the fixed spiral wall 15b. The bushing 22 thus oscillates about the eccentric shaft 20 in the second swinging direction R2 until the movable spiral wall 16b contacts the fixed spiral wall 15b. The clearance between the inner circumferential surface 13b of the receiving wall 13a and the portion of the outer circumferential surface of the counterweight 21 close to the first edge 21c is reduced.

The movable spiral wall 16b needs to be arranged without contacting the fixed spiral wall 15b so as to mount the movable scroll 16 to the fixed scroll 15. [ Therefore, when the movable scroll 16 is mounted on the fixed scroll 15, the bushing 22 is oscillated about the eccentric shaft 20 in the first swinging direction R1. At this time, if the bushing 22 is slightly oscillated about the eccentric shaft 20 in the first swinging direction R1, the movable spiral wall 16b can be positioned without contacting the fixed spiral wall 15b . This provides a relatively sufficient space between the inner circumferential surface 13b of the receiving wall 13a and the portion of the outer circumferential surface of the counterweight 21 close to the second edge 21d.

According to the present embodiment, the counterweight 21 has a radially extending portion 21a extending radially outward from the first imaginary circle C1 in the portion on the leading side in the first swinging direction R1. The amount of extension of the radially extending portion 21a extending radially outward from the first imaginary circle C1 is increased toward the leading side in the first swinging direction R1. Therefore, as compared with the case where the outer circumferential surface of the counterweight 21 extends entirely along the first imaginary circle C1, the size of the counterweight 21 is smaller than the size of the counterweight 21 and the inside of the receiving wall 13a So as to effectively utilize the space between the circumferential surfaces 13b. The counterweight 21 having an enlarged size adequately compensates for the centrifugal force acting on the movable scroll 16 when the movable scroll 16 reciprocates. This reduces the amount of unbalance of the movable scroll 16.

The illustrated embodiment achieves the following advantages.

(1) The counterweight 21 has a radial extension 21a extending radially outward from the first imaginary circle C1. The radially extending portion 21a is formed in a direction in which the bushing 22 rocks so as to reduce the distance between the center L2 of the bushing 22 and the rotation axis L1 of the rotary shaft 18, (R1) on the leading side. Therefore, as compared with the case where the outer circumferential surface of the counterweight 21 extends entirely along the first imaginary circle C1, the size of the counterweight 21 is smaller than the size of the counterweight 21 and the inside of the receiving wall 13a So as to effectively utilize the space between the circumferential surfaces 13b. The counterweight 21 having an enlarged size adequately compensates for the centrifugal force acting on the movable scroll 16 when the movable scroll 16 reciprocates. This reduces the amount of unbalance of the movable scroll 16 without enlarging the size of the scroll compressor 10. [

(2) The outer circumferential surface 21b of the radial extension 21a extends onto a second imaginary circle C2 having a larger diameter than the first imaginary circle C1. The center P2 of the second virtual circle C2 is displaced from the center L2 of the bushing 22 in the first swinging direction R1. The amount of extension of the radially extending portion 21a extending radially outward from the first imaginary circle C1 is increased toward the leading side in the first swinging direction R1. Thus, the shape of the counterweight 21 is simplified and the size of the counterweight 21 is expanded in a balanced manner. Therefore, it is possible to effectively use the space between the counterweight 21 and the inner circumferential surface 13b of the receiving wall 13a.

(3) According to the present embodiment, it is not necessary to expand the accommodating space for the counterweight 21 inside the receiving wall 13a so as to enlarge the size of the counterweight 21 to make it larger than the existing space. Therefore, it is possible to extend the size of the counterweight 21 without enlarging the size of the scroll compressor 10. [

The above-described embodiment may be modified into the following forms.

As shown in Fig. 3 according to the second embodiment, the counterweight 21 is provided with at least a part of the radial direction extending radially outward from the first imaginary circle C1 at the portion on the leading side in the first swinging direction R1, And has an extended portion 21a. In this case, the counterweight 21 includes a first outer circumferential surface 211 extending along the first imaginary circle C1 and a second outer circumferential surface 212 of the radial extension 21a. The second outer circumferential surface 212 is continuous with the first outer circumferential surface 211. The shape of the counterweight 21 is not limited to a specific shape as long as the space between the counterweight 21 and the inner circumferential surface 13b of the receiving wall 13a is effectively used.

In the illustrated embodiments, the center (the center L2 of the bushing 22) of the first imaginary circle C1 and the center P2 of the second imaginary circle C2 are aligned with the first edge 21c 2 < / RTI > edge 21d.

In the illustrated embodiments, the first edge 21c need not be located on the first virtual circle C1. In other words, the first virtual circle C1 does not need to be located inside the second virtual circle C2 while contacting the second virtual circle C2 at the first edge 21c.

In the illustrated first embodiment, the amount of extension of the radially extending portion 21a extending radially outward from the first imaginary circle C1 gradually increases toward the leading side in the first swinging direction R1. The amount of extension of the radial extension 21a may then be set to gradually increase.

In the illustrated embodiments, the counterweight 21 need not be integrally formed with the bushing 22. The counterweight 21, which is a separate member from the bushing 22, can be fixed to the bushing 22.

In the illustrated embodiments, the fixed scroll 15 need not be integrally formed with the center housing member 12. The stationary scroll 15, which is a separate member from the center housing member 12, can be fixed inside the center housing member 12. [

In the illustrated embodiments, the rotary shaft 18 can be rotationally driven by the driving force of the electric motor.

Accordingly, the embodiments and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be varied within the equivalents and scope of the appended claims.

Claims

A scroll compressor comprising:
A fixed scroll fixed to the housing and having a fixed spiral wall;
A movable scroll having a movable spiral wall engaging the fixed spiral wall;
A compression chamber for compressing refrigerant by reducing the volume of said compression chamber by orbital movement of said movable scroll relative to said fixed scroll;
A rotary shaft rotatably supported by the housing;
An eccentric shaft extending from the rotary shaft of the rotary shaft to a position displaced from the rotary shaft toward the movable scroll;
A bushing fitted to the eccentric shaft and rotating about the eccentric shaft; And
And a counterweight integrally formed with the bushing;
The housing having an inner circumferential surface having a center coinciding with the axis of rotation of the rotary shaft, the housing having a receiving wall for receiving the counterweight,
The bushing rotates about the eccentric shaft in a first swinging direction and in a second swinging direction opposite to the first swinging direction,
The bushing having a center set so as to gradually approach the rotation axis of the rotary shaft when the bushing swings in the first swinging direction,
Wherein the counterweight has at least a radial extension extending radially outwardly from a first imaginary circle having a center in the portion on the leading side in the first swinging direction and a center of the bushing.

The method according to claim 1,
Wherein an outer circumferential surface of the radial extension extends along a second imaginary circle having a larger diameter than the first imaginary circle,
The center of the second virtual circle is displaced from the center of the bushing in the first swinging direction,
Wherein an amount of extension of the radial extension extending radially outward from the first imaginary circle is increased toward the leading side in the first oscillation direction.

3. The method of claim 2,
Wherein the circumferentially opposite ends of the counterweight, the center of the first imaginary circle, and the center of the second imaginary circle are arranged on a common line.